Apparatus for analyzing various gases in the exhaust of motor vehicles has been in use for a number of years. Typically, such apparatus includes sensors for detecting the amount of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust. The sensors convert the concentration of the gases into a corresponding electrical signal which is processed by electronic circuitry and displayed either on a CRT screen or a meter.
More recently, it has been found advantageous to include in such apparatus the ability to detect the amount of oxygen (O.sub.2) in the vehicle exhaust. Unfortunately, commercial oxygen sensors are much slower acting than corresponding commercial HC or CO sensors. While a display of HC or CO concentration can generally be obtained in approximately 8 seconds, it frequently takes 16 seconds or longer for the oxygen sensor and its related circuitry to create a display of the concentration of oxygen. The delay in creating the oxygen display is confusing to the operator of the apparatus, especially when he receives the display of the HC and CO concentrations at an earlier time.
There have been attempts in the past to speed up the display of oxygen concentration in gas analyzing apparatus. For example, in U.S. Pat. No. 4,030,349 (Blanke et al.--June 21, 1977), the first derivative of the oxygen signal is displayed in order to obtain an advanced indication of the value of the oxygen signal itself. Although this approach may be a step in the right direction, it still does not provide an adequate display of the concentration of O.sub.2 within the same time period as the corresponding HC or CO displays.
In order to provide an improved analyzer, the applicants have taken an entirely new approach. They generate a resulting signal proportional to the sum of: (1) a first value proportioned to the oxygen sensor output, (2) a second value proportional to the first derivative of the oxygen sensor output and (3) a third value proportional to the second derivative of the oxygen sensor output. They have surprisingly discovered that by summing these three types of values, they can accurately predict the concentration of oxygen in the exhaust of a vehicle at a much earlier time than previously has been possible.
Accordingly, it is principal object of the invention to provide improved apparatus for anticipating or predicting the concentration of a gas, such as oxygen, at a rapid rate.
Another object of the invention is to provide apparatus of the foregoing type in which values of the oxygen signal and derivatives thereof are summed by electrical circuitry.
Another object of the invention is to provide apparatus of the foregoing type in which a three pole filter is utilized in order to more accurately predict the concentration of the gas.